The present invention relates to a fuel cell system suitably used for a moving body such as an automobile, more particularly to a fuel cell system capable of stably supplying fuel gas from an evaporator to a reforming reactor.
A fuel cell system for use in a moving body, which is mounted on an automobile and the like, is constituted by a fuel reforming portion for generating hydrogen-rich gas by reforming fuel such as methanol and the like; and a fuel cell portion for allowing the hydrogen-rich gas generated by the fuel reforming portion to react with oxygen-containing gas separately supplied from an air supply apparatus to generate electricity. The fuel reforming portion is constituted by an evaporator for evaporating fuel gas by use of heat generated in burning exhaust; and a reforming reactor for reforming the fuel gas evaporated by the evaporator actually into hydrogen-rich gas.
To allow the fuel cell system to behave with high efficiency and stability, the fuel gas must be stably supplied from the fuel reforming portion to the fuel cell portion, and, in the fuel reforming portion, the fuel gas must be stably supplied from the evaporator to the reforming reactor.
By the way, when a flow rate of the exhaust supplied to a combustor changes due to a load change of a fuel cell, a quantity of the exhaust from a fuel electrode of the fuel cell portion is made to change, and the temperature of the combustor is controlled. Thus, the temperature of the evaporator is kept constant, and a quantity of the fuel gas supplied to the fuel cell portion is maintained. A method to control the supply quantity of the fuel gas by the temperature of the combustor disclosed, for example, in Japanese Patent Laid-Open No. 10-106607 has been known. In this conventional technology, provided are pass lines which branch away from corresponding exhaust gas lines to guide the exhaust from the fuel cell portion to the combustion chamber and allow the exhaust to bypass the corresponding exhaust gas lines, and flow rate control valves are provided on the respective exhaust gas lines on downstream sides from branch points to adjust a flowing quantity of the exhaust flowing into a combustor.
No consideration for a change of boiling point temperature due to operation pressures of an evaporator and a combustor is taken in the conventional fuel cell systems for use in the moving body, and the evaporator and the combustor are controlled so as to aim at a target temperature of the combustor.
For this reason, even when the temperature of the combustor exceeds a target controlled temperature, a situation that the evaporator does not reach the target temperature so that an enough amount of fuel gas required by a fuel cell portion cannot be supplied to the reforming reactor may occur.
The present invention was invented in consideration of the above described problems of the conventional technology, and the object of the present invention is to provide a fuel cell system capable of stably supplying fuel gas from an evaporator to a reforming reactor.
To achieve the above described object, the fuel cell system of the present invention comprises a fuel tank for storing fuel; an evaporator for evaporating said fuel to generate fuel gas; a reforming reactor for generating reforming gas containing hydrogen from the fuel gas; a combustor for burning any one of the fuel and the reforming gas to supply heat to the evaporator; a fuel cell portion for generating electricity by use of the hydrogen contained in the reforming gas generated in the reforming reactor; a boiling point temperature estimation portion for estimating a boiling point temperature of the fuel in the evaporator based on an operation pressure of the evaporator; a vapor temperature measuring portion for measuring a vapor temperature of fuel gas in the evaporator; and a flow rate control portion for increasing a flow rate of any one of fuel and reforming gas burnt in the combustor when a value obtained by subtracting the boiling point temperature from the vapor temperature becomes below a predetermined value.
In other words, the fuel cell system of the present invention comprises a fuel tank for storing fuel; an evaporator for evaporating said fuel to generate fuel gas; a reforming reactor for generating reforming gas containing hydrogen from said fuel gas; a combustor for burning any one of said fuel and said reforming gas to supply heat to said evaporator; a fuel cell portion for generating electricity by use of said hydrogen contained in said reforming gas generated in said reforming reactor; boiling point temperature estimating means for estimating a boiling point temperature of said fuel in said evaporator based on an operation pressure of said evaporator; and vapor temperature measuring means for measuring a vapor temperature of fuel gas in said evaporator, wherein provided is flow rate control means for increasing a flow rate of any one of the fuel and the reforming gas burnt in said combustor when a value obtained by subtracting said boiling point temperature from said vapor temperature becomes below a predetermined value.
Beside, a method of controlling a fuel cell system of the present invention includes a fuel tank for storing fuel; an evaporator for evaporating said fuel to generate fuel gas; a reforming reactor for generating reforming gas containing hydrogen from said fuel gas; a combustor for burning any one of said fuel and said reforming gas to supply heat to said evaporator; a fuel cell portion for generating electricity by use of said hydrogen contained in said reforming gas generated by said reforming reactor; a boiling point temperature estimating portion; a vapor temperature measuring portion; and a flow rate control portion, said method comprising: estimating by use of said boiling point temperature estimating portion a boiling point temperature of said fuel in said evaporator based on an operation pressure of said evaporator; measuring by use of said vapor temperature measuring portion a vapor temperature of the fuel gas in said evaporator; and increasing a flow rate of any one of the fuel and the reforming gas burnt in said combustor when a value obtained by subtracting said boiling point temperature from said vapor temperature becomes below a predetermined value.
In this fuel cell system, since the boiling point temperature of the fuel is estimated based on the operation pressure in accordance with a state of the operation pressure of the fuel cell portion, it is possible to comply with a change in the boiling point temperature of the fuel gas due to a change in the operation pressure. Moreover, since a control is performed by a difference between the boiling point temperature and the vapor temperature, it is possible to supply the fuel gas of a necessary flow rate to the fuel cell portion sufficiently and effectively. At the same time, a large amount of fuel that has not been vaporized yet is never stored in the evaporator, and the fuel that has been vaporized yet does not get discharged with the fuel gas.